Retinoic acid (RA) is a potent cleft palate-inducing teratogen in rodents, and has been implicated in human teratogenesis. RA is thought to act through specific receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), that act as sequence-specific DNA-binding transcription factors. We have obtained preliminary data indicating that RXR-alpha plays a role in the induction of cleft palate following a teratogenic insult with retinoic acid during early palate organogenesis. This grant proposes to elaborate on these studies by identifying interactions between RXR-alpha and the RARs at the organismal, cellular and molecular levels during retinoid-induced teratogenesis. The objectives of this proposal, addressed in three specific aims outlined below, are to identify RARs that interact with RXR-alpha to mediate the teratogenic effect of RA on palate development, to examine the role of these receptors in inhibition of palate mesenchymal cell proliferation and epithelial differentiation, cellular processes important in RA- induced palatal clefting, and to investigate the role of specific RARs in RA-induced transforming growth factor beta (TGF-beta) gene expression. Specific aim number 1 proposes to determine, using gene knock-out mice, which, if any, of the RARs, RAR-alpha, RAR-beta or RAR-gamma, interact with RXR-alpha to mediate the teratogenic effect of retinoic acid (RA) on murine palate development. In Specific Aim number 2 we will examine the role of the RARs, in association with RXR-alpha, in mediating the inhibitory effect of RA on mesenchymal cell proliferation in vitro and in vivo, and on differentiation of the palatal medial edge epithelium in vivo. Specific aim number 3 will determine the role played by RXR-alpha and the RARs in retinoid-induced modulation of TGF-beta gene expression in vivo and in vitro. Regulation of TGF-beta mRNA and protein will be assayed by northern blotting, immunohistochemistry and bioassay. The data generated by this work will contribute to our understanding of retinoid-induced palatal clefting, and constitute the basis for an expanded study of the molecular mechanisms by which retinoic acid acts through the RXR-alpha/RAR signal transduction pathway. Research on the molecular mechanisms by which known teratogens produce malformations is important both for our understanding of the particular teratogenic processes, and also for the insights obtained on normal development and how it may be subverted by teratogens.